A known form of hydraulically trippable check valve has a poppet which is arranged in the valve body, is biased in the closing direction by a spring and, to relieve pressure on the high-pressure side of the hydraulic system, is liftable off its seat, against the restoring force of the closing spring, by a control piston which is arranged in the valve body and which can be acted on by a hydraulic control pressure, the control piston being provided with a piston plunger acting against the poppet at the latter's discharge end. A hydraulically pilot-controlled check valve of this kind is known from DE 3407878 C1.
In the closed position, such a check valve can serve as a safeguard for the hydraulic prop or props (when set) of a self-advancing support, and, in conjunction with control valves connected, in the gate, to the pressure and return lines of the longwall face power hydraulic system, as a setting valve and also as a recovery valve, the check valve when functioning as a recovery valve being tripped against its spring force by the hydraulic control piston to connect the pressure chambers of the prop or props, which are at high operating pressure, to the return. In the recovery operation, tripping of the check valve is effected by the control piston, acted on by the same high hydraulic pressure of the central longwall face pressure line as that with which the hydraulic props of the self-advancing support are set in the setting operation. Harmful oscillation and chatter of the check valve poppet when opened for the recovery operation are prevented by providing a spring-loaded restrictor in the connection between the back of the valve poppet and the side of the check valve connected to the prop pressure chambers. When the check valve is tripped, the discharge side of the check valve poppet is initially subject to the high operating pressure present in the prop pressure chambers, which is usually around 350-450 bar. This pressure acts in the restoring direction on the control piston and its plunger, which may cause oscillation and chatter of the control piston. To suppress this oscillation and chatter, the control piston needs to have a large diameter, and has to be subjected to a correspondingly high control pressure.